Parse flags that use "flag" package

It appears that Cobra will not automatically parse these flags, as it
does with those declared via its own API. This avoids warnings from the
glog package about logging before flag parsing.

main.go

@@ -46,6 +46,7 @@ func init() {
 }
 
 func main() {
+	flag.Parse()
 	rootCmd.PersistentFlags().AddGoFlagSet(flag.CommandLine)
 	if err := parseGoBuildFlags(rootCmd.PersistentFlags()); err != nil {
 		glog.Error(err)